The present invention relates to a hollow universal joint and in particular to a double hollow universal joint adapted to protectively house cabling extending through the joint and/or utilizing a stiffening material limiting buckling of the joint.
Universal joints have been used to interconnect working sections of a pig train used to inspect pipelines. In particular, the universal joints may be used in a pig train to interconnect the tow section to a magnetizing section, between magnetizing sections and to connect the magnetizing section with downstream recording and control devices. The universal joints used in this application typically comprise two coupled shafts that extend along the axis of the pipeline when the pig is moving along a straight path in the pipeline.
The universal joint is useful in allowing sections of the pig train to negotiate around bends in the pipe. However, this type of universal joint does not protect any cabling that extends between sections of the pig train. This cabling may wear when rubbing against the inside walls of the pipeline particularly when the pig train is negotiating a sharp bend in the pipe line. Also, the joint, particularly when configured as a double universal joint, has a tendency to buckle causing potential collision of adjacent sections of the pig train. While the joint is designed to negotiate bends in the pipeline any buckling of the joint in straight sections of a pipeline introduces error into the magnetically sensed readings of two magnetizer sections coupled by the joint.
Accordingly, there is a need to for a universal joint that is either able to protect cabling extending between sections coupled by the joint and/or is able to reduce axial freeplay between pig sections coupled by the universal joint.